The present invention relates mainly to the reconstitution or reconstruction of an object, especially of an object or component which is a composite or made of a composite material, which has a defect, to be treated or repaired, which affects at least its surface or even its entire thickness.
More specifically, the invention relates to the reconstitution or reconstruction or repair of objects as defined above by placing in or on the said defect, on the one hand, mechanically strong, continuous or staple fibres which are organized, for example in the form of a web or technical fabric, or are not organized, for example loose or in the form of a nonwoven, and, on the other hand, a polymeric material or resin (a single resin or a polymer alloy) which is thermoplastic or crosslinkable, especially thermocrosslinkable or thermosetting, this all forming, in the solid state, a matrix in which the said fibres are distributed or spread. By way of example, the fibres are glass, carbon or kevlar fibres, and the resin is an epoxy or polyester or phenolic or bismaleimide resin. These fibres may be put into the defect separately from the resin, in which case the said fibres are placed in the said defect, for example, in the form of superposed layers of fabric, and then the resin is injected into the mass of fabric in liquid form, or concomitantly, in which case a ready-to-use composite material is used, for example a prepreg material having a reinforcement consisting of the aforementioned fibres and a matrix of the resin, for example a partially crosslinked or uncrosslinked resin.
In both cases, the structure obtained on or in the defect is called monolith or monolithic, since it forms one piece in the solid state, without it being possible in practice to separate, for example by delamination, the aforementioned components, namely the fibres or layers on the one hand and the resin on the other.
For the purposes of the present description, and in the claims, unless otherwise indicated the term xe2x80x9ccompositexe2x80x9d refers to a structure, an object or a material consisting in a uniform manner of the assembly of several elementary materials or components, namely and especially fibres and resins, bonded together, and together having properties, especially mechanical properties, that no component has just by itself.
In practice, throughout the present description, the term xe2x80x9cresinxe2x80x9d refers to polymeric materials, which may be qualified, as is customary, by the term of adhesive or glue, for example a structural adhesive, whether these be thermoplastic or thermosetting plastics.
According to document DE-A-4,019,744, and more particularly according to the embodiment in FIG. 7 of that document, a process has been described for reconstituting or reconstructing an object, for example a composite object, having a defect which affects at least its surface. According to that process:
axe2x80x94at least one added piece or material, the shape and dimensions of which are matched to those of the said defect, is placed in or on this defect, this piece or this material comprising mechanically strong, continuous or staple fibres which may or may not be organized; for example, a superposition of fabric layers, collecting the mechanically strong fibres in an organized manner, is placed in this defect.
bxe2x80x94a polymer material, or resin, is placed in or on this defect in order to obtain a plastic matrix in which these fibres are distributed; for example, this polymer material is brought into the defect in liquid form and under pressure, thus impregnating the aforementioned fibres and obtaining, after the polymer material has cured, a solid plastic matrix in which these fibres are distributed,
cxe2x80x94a gas-draining means, for draining the gases given off by the plastic matrix during step (d) below, and a gas-extraction cover are placed, in succession and one on top of the other, on the added piece that was impregnated with the plastic matrix, which together with the rest of the object being reconstructed or repaired form an enclosure which is sealed with respect to the external atmosphere and circumscribes the defect and the added piece; by way of example, the venting means consists of a gas-draining textile web,
dxe2x80x94while evacuating the sealed enclosure, the added piece is heated using a radiant source, the emission from which comprises infrared radiation, and placing this source with respect to the aforementioned defect so as to irradiate the cover for extracting the gases given off by the plastic matrix.
Document DE-A-4,019,744 has described the abovementioned process only for treating or repairing solid objects made of one and the same material, to the exclusion of any other object.
Moreover, at the present time, in order to repair a monolithic composite object, for example in the aeronautical industry, the process employed is carried out in the following manner, with reference to FIG. 1 which is an exploded and diagrammatic view:
one or more pieces 2, or a material, the shape and dimensions of which are matched to those of the defect 1a to be repaired or filled, are prepared, especially by cutting; this material or these pieces, either assembled or superimposed one with respect to another, are themselves made of a composite material in the sense in which they combine, in a bonded manner, a plastic matrix and mechanically strong, continuous or staple fibres which may or may not be organized, for example made of carbon, kevlar, glass, etc. . . ;
the piece or pieces 2, or the material thus prepared, is or are added in or on the defect 1a in the treated object;
the following are placed in succession on the piece 2 and on the object 1, on each side of the defect and one on top of another:
a perforated or unperforated film 9, which does not adhere to the subsequently treated, for example crosslinked, added piece 2;
a gas-draining textile web 3 for draining, via it peripheral border 3a, the gases which will be given off by the plastic matrix during its treatment, for example its crosslinking;
a film 8 impermeable to the plastic;
a cover-shaped flexible heating structure 10 having, in general, electrical heating elements embedded in an electrically insulating material, for example a silicone;
a layer 11 for thermal insulation with respect to the outside;
and a flexible gas-extraction cover 4, forming, using suitable means 12 (for example seals), with the rest of the object 1 an enclosure 5 which is sealed with respect to the external atmosphere; this enclosure circumscribes not only the defect 1a and the added piece 2, but also all the superimposed elements described above.
The extraction cover 4 is evacuated, for example using a pump 13, and the flexible heating structure is connected to an electrical supply 14.
Using suitable control means, especially temperature sensors, the plastic matrix is thermally treated, for example thermally crosslinked, in the case in which the said plastic matrix is a crosslinkable or thermosetting polymer. The heat treatment is closely controlled, especially depending on the nature of the plastic matrix and on the desired mechanical performance.
The present invention relates to the reconstitution or reconstruction of composite objects, of the sandwich type, i.e. object having a solid cellular layer, for example a material of the xe2x80x9choneycombxe2x80x9d type, made of various materials such as board impregnated with a phenolic resin, made of plastic, or made of metal, or made of a structural plastic foam. This cellular layer is bonded, in a structural manner, at least on one side to a monolithic layer, as defined above, that is to say combining, in a monobloc manner, a plastic matrix and mechanically strong fibres distributed in the said matrix.
At the present time, no satisfactory solution exists, or even any solution at all, for repairing or reconstructing sandwich-type composite objects, particularly when only one face of the said object is accessible.
In practice, in order to reconstruct or reconstitute such an object, for example the upper surface part of an aircraft wing having a sandwich composite structure, the defect is firstly machined in order to give it a regular or controlled geometry. A resin or an adhesive is then placed at the bottom of the machined defect, followed by an added piece made of cellular material, this piece being fitted into the cellular layer of the object to be repaired, together with a resin for bonding to the rest of the cellular layer; and finally mechanically strong fibres and a plastic matrix are placed on the monolithic layer of the object to be repaired, in order to reconstitute the said layer at the defect.
The heat supply and the pressure that are required to bond and assemble all of the materials or pieces filling the defect, and those materials or pieces to the rest of the object to be reconstituted or reconstructed, are obtained by a procedure carried out once or several times, according to the following operating steps:
a gas-draining textile web, for draining, via its peripheral border, the gases given off by the plastic matrix during the step below, a cover-shaped flexible heating structure, having electrical heating elements embedded in an electrically insulating material (for example a silicone), and a cover for extracting the said gases are placed, in succession and one on top of the other, on the repaired object at the defect, which together with the rest of the object form an enclosure which is sealed with respect to the external atmosphere and circumscribes the defect and the pieces and materials which have been added thereto;
while evacuating the sealed enclosure, the added pieces and materials, together with the flexible heating structure, are heated in order, in the case of a thermocrosslinkable resin, to generate or initiate the crosslinking of the plastic matrix.
In the case of a composite object having one face inaccessible, for example the inner face, there are no solutions for thermally treating the resin at the bottom of the defect other than:
by overheating, using the flexible heating structure, around the core of the defect in order to try to thermally reach the inner face; but such overheating, apart from the fact that it is not very effective, is liable to damage the outer face of the object to be repaired; or else the flexible heating structure, or the object, has to be cooled around the periphery
removing the object, in order to gain access to its inner face, or replacing the object to be repaired, something which in some cases is not possible, or is at the very least economically punitive.
In the first case, when the required temperature cycle for crosslinking the resin at the bottom of the defect is not provided, this crosslinking does not take place or is imperfect, in such a way that the entire reconstruction of the object is compromised.
The essential object of the present invention is therefore to find a solution to the reconstruction or reconstitution of a composite object of the sandwich type.
According to the present invention, contrary to all expectations, it has been discovered that the use of a radiant source emitting infrared radiation, placed with respect to the defect to be treated so as to irradiate the cover for extracting the gases given off by the plastic matrix, made it possible to heat beyond the cellular layer of the sandwich composite object, with respect to the said extraction cover, this being so notwithstanding the thermal resistance normally presented by any cellular layer.
According to the invention, when the composite object comprises a solid cellular layer, for example of the honeycomb type, a first resin is deposited at the bottom of the defect, a cellular replacement part, for example of the honeycomb type, is then inserted, a second resin is deposited on the exposed part of the aforementioned cellular part together with at least one piece of a fabric of continuous or staple fibres, and at least one step consisting of the following operations is carried out:
a gas-draining means, for example a textile web, for draining the gases given off by the plastic matrix during the step below, and a cover for extracting the said gases are placed, in succession and one on top of the other, on the added piece, which together with the rest of the object form an enclosure which is sealed with respect to the external atmosphere and circumscribes the defect and the added piece,
while evacuating the sealed enclosure, the added piece, especially the cellular replacement part, is heated only using a radiant source emitting infrared radiation, and placing the said source with respect to the treated defect so as to irradiate the cover for extracting the gases given off by the plastic matrix.
The present invention also relates to the following methods of implementation:
The process for reconstituting or reconstructing the treated object comprises a single step, in which case, for example, the first resin requires a treatment temperature, for example a crosslinking temperature, which is lower than the treatment temperature, for example the crosslinking temperature, for the second resin.
The same process may be carried out in two steps, namely a first step during which a resin is deposited at the bottom of the defect, the cellular replacement part, for example in honeycomb form, is inserted and the two operations defined above are carried out; and a second step in which this resin, i.e. the same resin, is applied to the exposed upper part of the cellular part and the two operations described above are carried out again.
Preferably the piece of fabric associated with the second resin which comprises the second resin forming a plastic matrix in which the continuous or staple fibres are distributed.
The resin, or each resin, is a thermocrosslinkable or thermoplastic polymer material.
The infrared radiation has a wavelength lies within a range of between 1 and 10 microns. By way of example, the radiant source comprises at least one catalytic burner.
The extraction cover is made from at least one material which is relatively transparent with respect to infrared radiation, for example made of polyamide.
Preferably, the first resin is deposited at the bottom of the defect with at least one other piece of a fabric of continuous or staple fibres; by way of example, the other piece of fabric is a composite, for example a prepreg, as it comprises the first resin forming a plastic matrix in which the continuous or staple fibres are distributed.
Preferably, the treated composite object of the sandwich type comprises the cellular layer between two monolithic layers.
The cellular layer and the cellular replacement part, i.e. the defect-filling cellular part, are made of a cellular material, for example a structural plastic foam, for example made of epoxy resin.
By way of indication, the gas-draining means may be a mesh, for example made of metal.